I think that the vbo data is from -1 to 1, the problem is that the triangle is not correct, it must be the half of the screen but it isn't, is more smaller.
How i can create a triangle that is half of the entire screen ? and how are related the vbo vertexes to the width and height of the screen?
my goal is be able to set the entire coordinate for example 800 if the width of the screen is 800 ecc....
is possible?
my viewport recreated always in the render loop is
glViewport(0.0, 0.0, 800, 600);